Side-by-side self-crimping elastic fiber and preparation method therefor

ABSTRACT

A type of side-by-side self-crimping elastic fiber and preparation method thereof are disclosed. The preparation method includes distributing compatible or partially compatible first fiber-forming polymer melts and second fiber-forming polymer melts, then the fiber is extruded from first spinneret holes and second spinneret holes on the same spinneret. The first fiber-forming polymer melts and the second fiber-forming polymer melts flow into the first spinneret holes through first and second distribution holes, and flow into the second spinneret holes through third and fourth distribution holes, wherein the four distribution holes are cylindrical holes of equal height, the ratio of the diameter of the first distribution holes to the diameter of the second distribution holes is (1.10-1.20):1, and the ratio of the diameter of the third distribution holes to the diameter of the fourth distribution holes is 1:(1.10-1.20).

CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is the national phase entry of International Application No. PCT/CN2020/095554, filed on Jun. 11, 2020, which is based upon and claims priority to Chinese Patent Application No. 201911351604.X, filed on Dec. 24, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention belongs to the field of polyester fiber, and more particularly, relates to a side-by-side self-crimping elastic fiber and preparation method therefor.

BACKGROUND

Crimp is an important indicator of fibers that affects textile processing and final product characteristics and application properties.

The side-by-side bicomponent composite fiber is important in the family of bicomponent composite fibers, which utilizes the difference in the heat shrinkage properties of two components to make the fiber bend away from the fiber axis, showing a permanent three-dimensional spiral crimp and obtaining a crimp similar to that of wool fibers. The crimp of the fiber does not require the texturing process of the crimp of ordinary thermoplastic fibers, avoiding the thermal damage of chemical fibers, therefore the fiber is usually called “self-crimping fiber”, also known as three-dimensional crimp fiber, wherein the crimp is long-lasting, stable and elastic, which makes the fabric have better elasticity, fluffiness and coverage. By changing the component high-polymer properties, cross-sectional shape, component distribution, component ratio, spinning draft and heat-setting process parameters, the side-by-side bicomponent composite fiber with different properties can be obtained, which has high application value due to an advantage of designable performance, therefore it is favored and valued by the fiber manufacturing industry.

Although the side-by-side bicomponent fiber is widely used in woven fabrics, when promoting wider application in the knitting field, a very difficult problem has arisen: because of the side-by-side bicomponent fiber forming a regular spiral crimp shape during heat shrinkage, the surface of the knitted fabric will appear random “stripe unevenness”, especially on plain knitted fabrics. This problem makes the side-by-side bicomponent fiber unable to be applied in many kinds of knitted products such as simulated silk knitted underwear fabrics, therefore, the side-by-side bicomponent fiber knitted fabrics were evaluated as low-grade products with unevenness, which seriously restricts the development and application of side-by-side bicomponent fiber knitted fabrics.

Therefore, it is of great significance to develop a side-by-side self-crimping elastic fiber and preparation method therefor to avoid the random “strip unevenness”.

SUMMARY

The primary object of the present invention is to provide a side-by-side self-crimping elastic fiber and preparation method therefor, so as to solve the problem of random “strip unevenness” in the prior art when the side-by-side self-crimping elastic fiber is applied in knitted fabrics. The present invention uses the coexistence of X (the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilament with a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 3:2 to 2:1) and Y (the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilament with a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 2:3 to 1:2) in a single fiber bundle, which breaks the neat left and right spiral shapes of a bundle of pure X or Y fibers due to the different shrinkage modes and shapes of two second fiber-forming polymer/first fiber-forming polymer side-by-side composite fibers with different mass ratio of the first fiber-forming polymer to the second fiber-forming polymer, thus solving the problem of “strip unevenness” in the knitted fabrics made from a bundle of pure X or Y fibers.

To this end, the technical schemes of the invention are as follows:

The method for preparing a side-by-side self-crimping elastic fiber, comprising: distributing a first fiber-forming polymer melt and a second fiber-forming polymer melt according to a specific spinning process, then the side-by-side self-crimping elastic fiber is extruded from spinneret holes m and spinneret holes n on the same spinneret;

wherein the distribution is to distribute the first fiber-forming polymer melt through distribution holes A while distribute the second fiber-forming polymer melt through distribution holes B into spinneret holes m, and distribute the first fiber-forming polymer melt through distribution holes C while distribute the second fiber-forming polymer melt through distribution holes D into spinneret holes n;

wherein the first fiber-forming polymer and the second fiber-forming polymer are compatible or partially compatible (after mixing the first fiber-forming polymer and the second fiber-forming polymer, wherein the compatibility between the two polymers is determined according to the change of the glass transition temperatures);

at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the second fiber-forming polymer melt differs from that of the first fiber-forming polymer melt by no more than 5% (wherein the apparent viscosity is determined by simulation, specifically using a rheometer to measure the apparent viscosity of the polymer melt at a specific temperature);

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of (1.10-1.20):1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:(1.10-1.20);

wherein the specific spinning process is a POY process, an FDY process, a POY-DTY process or a POY-DT process, wherein the POY process, the FDY process and the POY-DT process are followed by a relaxation heat treatment of the fiber.

Specifically, the present invention comprises that distributing the first fiber-forming polymer melt through distribution holes A and C, and the second fiber-forming polymer melt through distribution holes B and D, and the apparent viscosity of the second fiber-forming polymer melt differs from that of the first fiber-forming polymer melt by no more than 5% at the entrance of distribution holes A, B, C and D, which are all cylindrical holes of equal height, and the ratio of the diameter of distribution hole A to the diameter of distribution hole B is not equal to the ratio of the diameter of distribution hole C to the diameter of distribution hole D, so that the mass ratio of the first fiber-forming polymer melt to the second fiber-forming polymer melt distributed to the spinneret m is different from the mass ratio of the first fiber-forming polymer melt to the second fiber-forming polymer melt distributed to the spinneret n, which realizes the coexistence of X and Y in a bundle of fibers, and ensures the different crimp shapes, accordingly, accordingly, the number and positional relationship of distribution holes and guide holes are reasonably set to ensure the smooth distribution; the present invention distributes all the spinneret holes m and n in concentric circles, and the spinneret holes on the same circle are all m or all n, to ensure that a part of Y can be mixed into the other part of X, breaking the formation of a neat left and right spiral shape; the present invention uses the common side-by-side composite spinneret holes without adjusting the shape of the spinneret holes; the present invention uses a specific spinning process, which can be compatible with the intrinsic viscosity of the first fiber-forming polymer melt and the intrinsic viscosity of the second fiber-forming polymer melt, to ensure that the apparent viscosities of the first fiber-forming polymer component and the second fiber-forming polymer component extruded from the spinneret are relatively close, thus not only controlling the mass ratio of the side-by-side composite monofilament, but also ensuring the smooth spinning, so the prepared fiber has excellent elasticity and comprehensive properties.

The principle of the present invention is as follows:

During the spinning process, the spinning melt is constantly flowing. In order to better control the flow of the melt, the calculation formula of the melt flow in the circular tube is based on the formula:

${{\Delta Q} = {\frac{\pi d^{4}}{128\mu l}\Delta P}},$

where ΔQ is the melt flow rate, d is the diameter of the circular tube, μ is the apparent viscosity of the melt at the entrance of the circular tube, l is the length of the circular tube, and ΔP is the pressure drop of the melt after passing through the circular tube, it can be seen from the formula that when ΔP, μ, and l are kept equal, the ratio of the melt flow rate flowing in the two circular tubes is close to the ratio of the fourth power of the diameter of the circular tube;

The present invention is distributing a first fiber-forming polymer melt and a second fiber-forming polymer melt according to a specific spinning process, then the side-by-side self-crimping elastic fiber is extruded from spinneret holes m and spinneret holes n on the same spinneret; wherein the distribution is to distribute the first fiber-forming polymer melt through distribution holes A while distribute the second fiber-forming polymer melt through distribution holes B into spinneret holes m, and distribute the first fiber-forming polymer melt through distribution holes C while distribute the second fiber-forming polymer melt through distribution holes D into spinneret holes n;

wherein the ratio of the first fiber-forming polymer melt flow through distribution hole A (or C) to the second fiber-forming polymer melt flow through distribution hole B (or D) is

${\frac{\Delta Q1}{\Delta Q2} = {\frac{\Delta P1d1^{4}}{\mu 1l1}\frac{{\mu 2}l2}{\Delta P2d2^{4}}}},$

where ΔQ1, d1, μ1, l1 and ΔP1 correspond to distribution hole A (or C), and ΔQ2, d2, μ2, l2, and ΔP2 correspond to distribution hole B (or D); since the apparent viscosities of the second fiber-forming polymer melt and the first fiber-forming polymer melt at the entrances of distribution hole A and distribution hole B are close to the same (the difference is less than 5%), and also the apparent viscosities of the second fiber-forming polymer melt and the first fiber-forming polymer melt at the entrances of distribution hole C and distribution hole D are close to the same (the difference is less than 5%), so μ1 and μ2 are approximately equal; at the entrance of distribution holes A, B, C and D, the apparent viscosity of the second fiber-forming polymer melt differs from that of the first fiber-forming polymer melt by no more than 5%, and distribution holes A, B, C and D are all set on the distribution plate with small size, therefore the pressure drop of the first fiber-forming polymer melt passing through distribution hole A is basically the same as that of the second fiber-forming polymer melt passing through distribution hole B, and the pressure drop of the first fiber-forming polymer melt passing through distribution hole C is basically the same as that of the second fiber-forming polymer melt passing through distribution hole D, so ΔP1 and ΔP2 are approximately equal; since distribution hole A and distribution hole B are of equal height, the distribution hole C and distribution hole D are equal in height, so l1 and l2 are equal;

wherein the calculation shows that,

$\frac{\Delta Q1}{\Delta Q2}$

is approximately equal to

$\frac{\Delta d1^{4}}{\Delta d2^{4}},$

since the ratio of the diameter of distribution hole A to that of distribution hole B is (1.10-1.20):1, so the ratio of the first fiber-forming polymer melt flow through distribution hole A to the second fiber-forming polymer melt flow through distribution hole B is about 3:2 to 2:1, and the mass ratio of the first fiber-forming polymer to the second fiber-forming polymer in the monofilament finally extruded from spinneret hole m is 3:2 to 2:1, similarly, since the ratio of the diameter of distribution hole C to that of distribution hole D is 1:(1.10-1.20), so the ratio of the first fiber-forming polymer melt flow through distribution hole C to the second fiber-forming polymer melt flow through distribution hole D is about 2:3 to 1:2, and the mass ratio of the first fiber-forming polymer to the second fiber-forming polymer in the monofilament finally extruded from spinneret hole n is 2:3 to 1:2;

In addition, the first fiber-forming polymer and the second fiber-forming polymer in the present invention have different heat shrinkage rates, further, by mixing the first fiber-forming polymer and the second fiber-forming polymer, the two polymers with different heat shrinkage rates are compatible or partially compatible, and the existence of compatibility allows the polymers to be bonded together when they pass through the same spinneret (that is, the two fiber-forming polymer melts are extruded after distribution by side-by-side composite spinning together), wherein the bonding effect together with different heat shrinkage effects, makes two polymer fibers coming out of the same spinneret hole (that is, the second fiber-forming polymer/first fiber-forming polyme side-by-side composite monofilament) to form a self-crimping shape after heat treatment, so as to have elasticity, wherein the self-crimping shape is specifically the fiber-forming polymer with a large heat shrinkage rate is on the inner side of the spiral crimp, and the fiber-forming polymer with a small heat shrinkage rate is on the outer side of the spiral crimp;

In the same bundle of fibers, a part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 3:2 to 2:1, and another part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 2:3 to 1:2, therefore, there is a certain difference in the crimp shape of different monofilaments, which plays the role of breaking the neat left and right spiral shapes of pure second fiber-forming polymer/first fiber-forming polymer side-by-side composite filament, so that the monofilament crimping directions of the prepared side-by-side self-crimping elastic fiber are randomly distributed after the relaxation heat treatment, therefore, the surface of the knitted fabric woven from the self-crimping elastic fiber will not appear random “stripe unevenness”.

The following preferred technology program is presented to give a detailed description for this invention.

In the method for preparing a side-by-side self-crimping elastic fiber, wherein the ratio of the mass of the second fiber-forming polymer melt to the mass of the first fiber-forming polymer melt is 50:50.

wherein the spinneret hole m or n is a circular, oval, or “8”-shaped spinneret hole, the present invention uses the common side-by-side composite spinneret holes without adjusting the shape of spinneret holes m or n.

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n, to make sure that Y (or X) can be mixed into X (or Y) and breaks the formation of a neat left and right spiral shape.

wherein the first fiber-forming polymer and the second fiber-forming polymer are of the same materials with different viscosities, or of different materials, and there must also be a difference in heat shrinkage between the polymers meeting these two conditions, after heat treatment, the fibers can form self-crimping shapes; wherein the materials of the first fiber-forming polymer and the second fiber-forming polymer are selected from polyester homopolymer, polyester copolymer, polyester modified product, polyamide homopolymer, polyamide copolymer and polyamide modified product.

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the second fiber-forming polymer melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the first fiber-forming polymer melt is transported through a spinning box II to the distribution hole A and the distribution hole C (wherein the intrinsic viscosity of the first fiber-forming polymer melt, the intrinsic viscosity of the second fiber-forming polymer melt, the temperature of the spinning box I, the temperature of the spinning box II, and the temperature of the spinning box III are compatible with each other, so that the apparent viscosities of the second fiber-forming polymer melt and the first fiber-forming polymer melt at the entrances of the distribution holes A to D are nearly the same).

wherein the relaxation heat treatment has a temperature of 90-120° C., and a time of 20 -30 min.

The side-by-side self-crimping elastic fiber prepared by any one of the above preparation methods, is composed of multiple second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments, and in the same bundle of fibers, wherein a part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 3:2 to 2:1, and another part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 2:3 to 1:2; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed after heat treatment, wherein the random distribution is a mathematical concept that each fiber has a different crimp shape than other fibers, thus the prepared fabric will not appear “stripe unevenness”.

Benefits:

(1) The preparation method of a side-by-side self-crimping elastic fiber in the present invention, wherein a part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 3:2 to 2:1, and another part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer to the second fiber-forming polymer of 2:3 to 1:2 in the same bundle of fibers, so that the monofilament crimping directions of each fiber are randomly distributed after the relaxation heat treatment, which makes each fiber has a different crimp shape than other fibers;

(2) The preparation method of a side-by-side self-crimping elastic fiber in the present invention, wherein the side-by-side self-crimping elastic fiber cannot form a regular arrangement of spiral crimp, thus solving the problem of “stripe unevenness” in the knitted fabric made from the side-by-side self-crimping elastic fiber;

(3) The preparation method of a side-by-side self-crimping elastic fiber in the present invention has excellent elasticity, good comprehensive properties, and broader application field.

BRIEF DESCRIPTION OF THE DRAWING

FIGURE is a schematic diagram of the melt distribution of the present invention; wherein A, B, C and D are mutually independent distribution holes, and E and F are mutually independent guide holes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Based on above mentioned method, the following embodiments are carried out for further demonstration in the present invention. It is to be understood that these embodiments are only intended to illustrate the invention and are not intended to limit the scope of the invention. In addition, it should be understood that after reading the contents described in the present invention, those technical personnel in this field can make various changes or modifications to the invention, and these equivalent forms also fall within the scope of the claims attached to the application.

The crimp shrinkage and crimp stability in the present invention are obtained by testing the tow by using GB6506-2001 “Synthetic fiber-Test method for crimp contraction properties of textured filament yarns”;

The text methods of the shrinkage elongation (reflecting the degree of elasticity and crimp of textured filament yarns, wherein the fibers are subjected to a light load and then to a heavy load, and the ratio of the difference in length to the curl length is calculated for both loads) and the crimp elastic recovery rate are as follows:

Firstly, cut two fiber samples of about 50 cm in length, put them into 100° C. hot water for 30 minutes, take them out and dry them naturally, next intercept a sample of about 30 cm in length, wherein fix one end and load another end with a load of 0.0018 cN/dtex for 30 seconds, and mark it at 20 cm, that is, the initial length li of the sample; then load another end with a load of 0.09 cN/dtex for 30 seconds, and measure the position of the marked point, which is the length l₂ of the sample under heavier load; finally remove the load and let the sample retract for 2 minutes, next add a load of 0.0018 cN/dtex for 30 seconds and measure the position of the marked point, which is the recovery length 13; the shrinkage elongation (CE) and the crimp elastic recovery rate (SR) are calculated as follows:

CE=(l ₂ −l ₁)/l ₁;

SR=(l ₂ −l ₃)/(l ₂ −l ₁).

Example 1

A method for preparing a side-by-side self-crimping elastic fiber, according to an FDY process, wherein a PET melt (intrinsic viscosity of 0.6 dL/g) and a PA6 melt (intrinsic viscosity of 2.2 dL/g) in a mass ratio of 50:50 are distributed and extruded from circular spinneret holes m and circular spinneret holes n on the same spinneret to obtain a fully drawn yarn, wherein the side-by-side self-crimping elastic fiber is prepared after the relaxation heat treatment;

wherein the PA6 melt and the PET melt each contains 5wt % of the PET-PA6 copolymer melt; wherein the preparation process of the PET-PA6 copolymer is as follows: the PET with a number average molecular weight of 2000 and the PA6 with a number average molecular weight of 2000 are mixed at a mass ratio of 1:1, then carrying out the polycondensation reaction at a temperature of 273° C. and a vacuum degree of 45 Pa for 60 min;

wherein the distribution is to distribute the PA6 melt through distribution holes A while distribute the PET melt through distribution holes B into spinneret holes m; and distribute the PA6 melt through distribution holes C while distribute the PET melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PET melt differs from that of the PA6 melt by 5%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.10:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.10;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

as shown in the figure, wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PET melt is transported through a spinning box I to the distribution hole B and the distribution hole D, while the PA6 melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 285° C., the temperature of the spinning box II is 270° C., and the temperature of the spinning box III is 282° C.;

wherein the FDY process involves technological parameters: a cooling temperature of 25° C., an interlacing pressure of 0.2 MPa, a godet roller 1 speed of 1600 m/min, a godet roller 1 temperature of 80° C., a godet roller 2 speed of 2760 m/min, a godet roller 2 temperature of 140 ° C., and a winding speed of 2710 m/min; wherein the relaxation heat treatment has a temperature of 104° C., and a time of 30 minutes;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PA6/PET side-by-side composite monofilaments; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 52%, a crimp stability of 80%, a shrinkage elongation of 88%, a crimp elastic recovery rate of 93%, a breaking strength of ≥2.5 cN/dtex, an elongation at break of 50.5%, and a total fineness of 100 dtex.

The prepared side-by-side self-crimping elastic fiber is made into the knitted fabric, which is tested for strip unevenness, and the test result is that the D value of the knitted fabric made of the side-by-side self-crimping elastic fiber is 0.57%; this indicates that the prepared side-by-side self-crimping elastic fiber in the present invention does not have the problem of “stripe unevenness”.

Example 2

A method for preparing a side-by-side self-crimping elastic fiber, according to an FDY process, wherein a PET melt (intrinsic viscosity of 0.63 dL/g) and a PA6 melt (intrinsic viscosity of 2 dL/g) in a mass ratio of 50:50 are distributed and extruded from oval spinneret holes m and “8”-shaped spinneret holes n on the same spinneret to obtain a fully drawn yarn, wherein the side-by-side self-crimping elastic fiber is prepared after the relaxation heat treatment;

wherein the PA6 melt and the PET melt each contains 5wt % of the PET-PA6 copolymer melt; wherein the preparation process of the PET-PA6 copolymer is as follows: the PET with a number average molecular weight of 2500 and the PA6 with a number average molecular weight of 2500 are mixed at a mass ratio of 1:1, then carrying out the polycondensation reaction at a temperature of 275° C. and a vacuum degree of 45 Pa for 55 min;

wherein the distribution is to distribute the PA6 melt through distribution holes A while distribute the PET melt through distribution holes B into spinneret holes m; and distribute the PA6 melt through distribution holes C while distribute the PET melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PET melt differs from that of the PA6 melt by 2.8%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.18:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.18;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PET melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the PA6 melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 283° C., the temperature of the spinning box II is 265° C., and the temperature of the spinning box III is 282° C.;

wherein the FDY process involves technological parameters: a cooling temperature of 23° C., an interlacing pressure of 0.24 MPa, a godet roller 1 speed of 1550 m/min, a godet roller 1 temperature of 80° C., a godet roller 2 speed of 2800 m/min, a godet roller 2 temperature of 144 ° C., and a winding speed of 2670 m/min; wherein the relaxation heat treatment has a temperature of 90° C., and a time of 24 minutes;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PA6/PET side-by-side composite monofilaments; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 51.5%, a crimp stability of 77.3%, a shrinkage elongation of 87.9%, a crimp elastic recovery rate of 92.8%, a breaking strength of ≥2.5 cN/dtex, an elongation at break of 57%, and a total fineness of 95 dtex.

The prepared side-by-side self-crimping elastic fiber is made into the knitted fabric, which is tested for strip unevenness, and the test result is that the D value of the knitted fabric made of the side-by-side self-crimping elastic fiber is 0.24%; this indicates that the prepared side-by-side self-crimping elastic fiber in the present invention does not have the problem of “stripe unevenness”.

Example 3

A method for preparing a side-by-side self-crimping elastic fiber, according to a POY-DT process, wherein a PET melt (intrinsic viscosity of 0.55 dL/g) and a PBT melt (intrinsic viscosity of 1.1 dL/g) in a mass ratio of 50:50 are distributed and extruded from circular spinneret holes m and oval spinneret holes n on the same spinneret to obtain a POY-DT yarn, wherein the side-by-side self-crimping elastic fiber is prepared after the relaxation heat treatment;

wherein the distribution is to distribute the PBT melt through distribution holes A while distribute the PET melt through distribution holes B into spinneret holes m; and distribute the PBT melt through distribution holes C while distribute the PET melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PET melt differs from that of the PBT melt by 4.9%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.15:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.15;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PET melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the PBT melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 280° C., the temperature of the spinning box II is 260° C., and the temperature of the spinning box III is 276° C.;

wherein the POY-DT process involves technological parameters: a cooling temperature of 23° C., a winding speed of 2800 m/min, a setting temperature of 133° C., a stretching temperature of 95° C., and a stretching multiplier of 1.8;

wherein the relaxation heat treatment has a temperature of 90° C., and a time of 30 minutes;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PBT/PET side-by-side composite monofilaments; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 66%, a crimp stability of 92.3%, a shrinkage elongation of 114%, a crimp elastic recovery rate of 80%, a breaking strength of 3.07 cN/dtex, an elongation at break of 47%, and a total fineness of 80 dtex.

Example 4

A method for preparing a side-by-side self-crimping elastic fiber, according to a POY process, wherein a PTT melt (intrinsic viscosity of 0.9 dL/g) and a PBT melt (intrinsic viscosity of 1.21 dL/g) in a mass ratio of 50:50 are distributed and extruded from circular spinneret holes m and circular spinneret holes n on the same spinneret to obtain the side-by-side self-crimping elastic fiber;

wherein the distribution is to distribute the PBT melt through distribution holes A while distribute the PTT melt through distribution holes B into spinneret holes m; and distribute the PBT melt through distribution holes C while distribute the PTT melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PTT melt differs from that of the PBT melt by 5%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.1:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.1;

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PTT melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the PBT melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 255° C., the temperature of the spinning box II is 266° C., and the temperature of the spinning box III is 265° C.;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

wherein the POY process involves technological parameters: a cooling temperature of 24° C., and a winding speed of 2660 m/min;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PBT/PTT side-by-side composite monofilaments; wherein the monofilament crimping directions of the DT yarn made from side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 70%, a crimp stability of 93.3%, a shrinkage elongation of 113%, a crimp elastic recovery rate of 85%, a breaking strength of 2.29 cN/dtex, an elongation at break of 125%, a monofilament fineness of 0.5dtex, and a total fineness of 110 dtex.

Example 5

A method for preparing a side-by-side self-crimping elastic fiber, according to a POY-DT process, wherein a PET melt (intrinsic viscosity of 0.52 dL/g) and a PBT melt (intrinsic viscosity of 1.14 dL/g) in a mass ratio of 50:50 are distributed and extruded from circular spinneret holes m and circular spinneret holes n on the same spinneret to obtain a POY-DT yarn, wherein the side-by-side self-crimping elastic fiber is prepared after the relaxation heat treatment;

wherein the distribution is to distribute the PBT melt through distribution holes A while distribute the PET melt through distribution holes B into spinneret holes m; and distribute the PBT melt through distribution holes C while distribute the PET melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PET melt differs from that of the PBT melt by 5%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.17:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.17;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PET melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the PBT melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 279° C., the temperature of the spinning box II is 261° C., and the temperature of the spinning box III is 277° C.;

wherein the POY-DT process involves technological parameters: a cooling temperature of 25° C., a winding speed of 3100 m/min, a setting temperature of 134° C., a stretching temperature of 89° C., and a stretching multiplier of 1.7;

wherein the relaxation heat treatment has a temperature of 98° C., and a time of 27 minutes;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PBT/PET side-by-side composite monofilaments; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 67%, a crimp stability of 92.6%, a shrinkage elongation of 114%, a crimp elastic recovery rate of 80%, a breaking strength of 3.02 cN/dtex, an elongation at break of 51%, and a total fineness of 140 dtex.

Example 6

A method for preparing a side-by-side self-crimping elastic fiber, according to a POY-DT process, wherein a PET melt (intrinsic viscosity of 0.51 dL/g) and a PBT melt (intrinsic viscosity of 1.14 dL/g) in a mass ratio of 50:50 are distributed and extruded from circular spinneret holes m and circular spinneret holes n on the same spinneret to obtain a POY-DT yarn, wherein the side-by-side self-crimping elastic fiber is prepared after the relaxation heat treatment;

wherein the distribution is to distribute the PBT melt through distribution holes A while distribute the PET melt through distribution holes B into spinneret holes m; and distribute the PBT melt through distribution holes C while distribute the PET melt through distribution holes D into spinneret holes n; at the entrance of distribution holes A, B, C and D, wherein the apparent viscosity of the PET melt differs from that of the PBT melt by 4.4%;

wherein the distribution holes A and B are equally-high cylindrical holes with a diameter ratio of 1.18:1, and the distribution holes C and D are equally-high cylindrical holes with a diameter ratio of 1:1.18;

wherein all the spinneret holes are distributed in concentric circles, and the spinneret holes on the same circle are all m or all n;

wherein the spinneret hole m comprises a guide hole E, a transition hole and a capillary micropore connected sequentially, the spinneret hole n comprises a guide hole F, a transition hole and a capillary micropore connected sequentially, the guide hole E is connected with a distribution hole A and a distribution hole B at the same time, and the guide hole F is connected with a distribution hole C and a distribution hole D at the same time; wherein the distribution holes A, B, C and D are located on the distribution plate in the spinning box III, the PET melt is transported through a spinning box Ito the distribution hole B and the distribution hole D, while the PBT melt is transported through a spinning box II to the distribution hole A and the distribution hole C;

wherein the temperature of the spinning box I is 279° C., the temperature of the spinning box II is 260° C., and the temperature of the spinning box III is 274° C.;

wherein the POY-DT process involves technological parameters: a cooling temperature of 25° C., a winding speed of 2840 m/min, a setting temperature of 135° C., a stretching temperature of 95° C., and a stretching multiplier of 1.7;

wherein the relaxation heat treatment has a temperature of 101° C., and a time of 26 minutes;

wherein the prepared side-by-side self-crimping elastic fiber is composed of multiple PBT/PET side-by-side composite monofilaments; wherein the monofilament crimping directions of the side-by-side self-crimping elastic fiber are randomly distributed; wherein the side-by-side self-crimping elastic fiber comprises mechanical performance indices: a crimp shrinkage of 68%, a crimp stability of 92.9%, a shrinkage elongation of 115%, a crimp elastic recovery rate of 82%, a breaking strength of 3.04 cN/dtex, an elongation at break of 49%, and a total fineness of 90 dtex. 

What is claimed is:
 1. A method for preparing a side-by-side self-crimping elastic fiber, comprising: distributing a first fiber-forming polymer melt and a second fiber-forming polymer melt according to a specific spinning process, then extracting from first spinneret holes and second spinneret holes on a same spinneret to obtain the side-by-side self-crimping elastic fiber; wherein a distribution is to distribute the first fiber-forming polymer melt through first distribution holes while distribute the second fiber-forming polymer melt through second distribution holes into the first spinneret holes, and distribute the first fiber-forming polymer melt through third distribution holes while distribute the second fiber-forming polymer melt through fourth distribution holes into the second spinneret holes; wherein the first fiber-forming polymer melt and the second fiber-forming polymer melt are compatible or partially compatible; at entrances of the first distribution holes, the second distribution holes, the third distribution holes, and the fourth distribution holes, wherein an apparent viscosity of the second fiber-forming polymer melt differs from an apparent viscosity of the first fiber-forming polymer melt by no more than 5%; wherein the first distribution holes and the second distribution holes are equally-high cylindrical holes with a diameter ratio of (1.10-1.20):1, and the third distribution holes and the fourth distribution holes are equally-high cylindrical holes with a diameter ratio of 1:(1.10-1.20); wherein the specific spinning process is a POY process, an FDY process, a POY-DTY process, or a POY-DT process, wherein the POY process, the FDY process, and the POY-DT process are followed by a relaxation heat treatment of the side-by-side self-crimping elastic fiber.
 2. The method of claim 1, wherein a ratio of a mass of the second fiber-forming polymer melt to a mass of the first fiber-forming polymer melt is 50:50.
 3. The method of claim 1, wherein each of the first spinneret holes or each of the second spinneret holes is a circular, oval, or “8”-shaped spinneret hole.
 4. The method of claim 1, wherein all the first spinneret holes and the second spinneret holes are distributed in concentric circles, and the spinneret holes on a same circle are all the first spinneret holes or all the second spinneret holes.
 5. The method of claim 1, wherein the first fiber-forming polymer melt and the second fiber-forming polymer melt are of same materials with different viscosities, or of different materials; wherein materials of the first fiber-forming polymer melt and the second fiber-forming polymer melt are selected from a polyester homopolymer, a polyester copolymer, a polyester modified product, a polyamide homopolymer, a polyamide copolymer, and a polyamide modified product.
 6. The method of claim 1, wherein each of the first spinneret holes comprises a first guide hole, a first transition hole, and a first capillary micropore connected sequentially, each of the second spinneret holes comprises a second guide hole, a second transition hole, and a second capillary micropore connected sequentially, the first guide hole is connected with the first distribution holes and the second distribution holes at the same time, and the second guide hole is connected with the third distribution holes and the fourth distribution holes at the same time; wherein the first distribution holes, the second distribution holes, the third distribution holes, and the fourth distribution holes are located on a distribution plate in a third spinning box III, the second fiber-forming polymer melt is transported through a first spinning box to the second distribution holes and the fourth distribution holes, while the first fiber-forming polymer melt is transported through a second spinning box to the first distribution holes and the third distribution holes.
 7. The method of claim 1, wherein the relaxation heat treatment has a temperature of 90-120° C., and a time of 20-30 min.
 8. A side-by-side self-crimping elastic fiber prepared by the method of claim 1, comprising multiple second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments, and in a same bundle of fibers, wherein a first part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer melt to the second fiber-forming polymer melt of 3:2 to 2:1, and a second part of the second fiber-forming polymer/first fiber-forming polymer side-by-side composite monofilaments have a mass ratio of the first fiber-forming polymer melt to the second fiber-forming polymer melt of 2:3 to 1:2.
 9. The side-by-side self-crimping elastic fiber of claim 8, wherein during a preparation of the side-by-side self-crimping elastic fiber, a ratio of a mass of the second fiber-forming polymer melt to a mass of the first fiber-forming polymer melt is 50:50.
 10. The side-by-side self-crimping elastic fiber of claim 8, wherein each of the first spinneret holes or each of the second spinneret holes is a circular, oval, or “8”-shaped spinneret hole.
 11. The side-by-side self-crimping elastic fiber of claim 8, wherein all the first spinneret holes and the second spinneret holes are distributed in concentric circles, and the spinneret holes on a same circle are all the first spinneret holes or all the second spinneret holes.
 12. The side-by-side self-crimping elastic fiber of claim 8, wherein the first fiber-forming polymer melt and the second fiber-forming polymer melt are of same materials with different viscosities, or of different materials; wherein materials of the first fiber-forming polymer melt and the second fiber-forming polymer melt are selected from a polyester homopolymer, a polyester copolymer, a polyester modified product, a polyamide homopolymer, a polyamide copolymer, and a polyamide modified product.
 13. The side-by-side self-crimping elastic fiber of claim 8, wherein each of the first spinneret holes comprises a first guide hole, a first transition hole, and a first capillary micropore connected sequentially, each of the second spinneret holes comprises a second guide hole, a second transition hole, and a second capillary micropore connected sequentially, the first guide hole is connected with the first distribution holes and the second distribution holes at the same time, and the second guide hole is connected with the third distribution holes and the fourth distribution holes at the same time; wherein the first distribution holes, the second distribution holes, the third distribution holes, and the fourth distribution holes are located on a distribution plate in a third spinning box III, the second fiber-forming polymer melt is transported through a first spinning box to the second distribution holes and the fourth distribution holes, while the first fiber-forming polymer melt is transported through a second spinning box to the first distribution holes and the third distribution holes.
 14. The side-by-side self-crimping elastic fiber of claim 8, wherein the relaxation heat treatment has a temperature of 90-120° C., and a time of 20-30 min. 